Legal Imperatives to Survive the Climate Crisis: Forethoughts on the ICJ Advisory Opinion

On July 23, 2025, the International Court of Justice provided its Advisory Opinion on “The Obligations of States in Respect of Climate Change.” Requested by the UN General Assembly in 2023 ( vide Resolution 77/276), the unanimous ruling is a landmark that will guide decision-making under International Law for decades to come as States cope with the impact's environmental degradation amidst rapidly warming temperatures. The Court characterized this growing crisis as “an existential problem of planetary proportions.” The Opinion for the first time makes clear that International Law addressed the entirety of the plant, and is a holistic body of treaty obligations and customary law duties. The Human Right to the environment girds these duties. A stringent duty of due diligence is required to fulfill theses substantive duties. While States will vary as they apply principles of law, including sustainable development, to observe their due diligence, none are exempt from doing their utmost to protect. Failures to do so have legal consequences under customary laws of State Responsibility. The Advisory Opinion applies to, and will guide decision-making under all multilateral environmental agreements (MEAs). To fulfill stringent due diligence, States are to implement national and international laws for environmental impact assessment (EIA), and other laws requiring use of Nature Based Solutions that protect biodiversity. The Opinion makes clear that States must discontinue reliance of fossil fuels. The Court's Opinion reflects the law set forth in the submissions of the International Union for the Conservation of Nature (IUCN). As States apply stringent due diligence, and national courts address legal claims regarding climate change, the Opinion will drive the progressive development of international climate law, from the lex lata expressed in the Opinion to the lex ferenda needed to protect all States and the planet.